Digg adds nofollow on some external links for better SEO

Digg started adding rel="nofollow" on some external links, to reduce the incentive to spammy posts (link spam), including all external links from comments, user profiles and story pages below a certain threshold of popularity. While the quality contents can still enjoy free ‘search engine juice’. This work was done in consultation with leading experts from the SEO/SEM and link spam fields.